When using whipped egg whites in a recipe, make sure all other ingredients are ready to go, as the beaten whites will start to deflate quickly.
4 egg whites at room temperature
¼ teaspoon cream of tarter
Make sure that there is not a trace of grease or egg yolk in your bowl. (Stainless-steel is best; plastic bowls tend to hold onto grease and glass bowls are too slippery to hold up the whites.) Use a bit of lemon juice or vinegar and a paper towel to wipe your equipment before starting.
Start mixing on a medium-low speed until the whites start to get foamy. This helps give them a strong structure.
Add the cream of tartar. Gradually increase speed to high until you reach the desired stiffness.
Soft peak stage: The whites are thickened but slightly droopy when the whisk is right side up. They should have a velvety sheen . You'd use these for a soufflé or a mousse. This is when you would add sugar if making meringues.
Stiff peak stage: The whites hold their peak when the whisk is right side up. They should also stay solid when the bowl is turned upside down, and still have that velvety sheen. You use stiff whites for meringues or foam-based cakes such as angel food cake.
Overbeaten egg whites: The white have lost the velvety sheen, look dry and grainy. They lose their puffing abilities.